Inside micrometer attachment



April 30, 1940- c. BIGWOOD 2,199,236 R INSIDE MICROMETER ATTACHMENT Filed May 18, 1939 a Y 6 INVENTOR.

C l 9 20/1 I flzlgwaad ATTORNEYS.

Patented Apr. 30,

were? fS'iATEs A PATENT OF-FiC-E MIGROMETER. ATTACHMENT curios sig a, Athol, Masa, assignor it The L. 'S. Starrett Company, Athol, Mass, at corporati'on of Massachusetts Application May s, 1939, Serial No. 214,343.

4 Claims. (01. 33-167) This invention relates to inside micrometer calipers and particularly to those having an end adjustability of gaging range or distance by means of supplemental extension rods used interchangeably with a micrometer head which gives fine readings within the limits of the length of its adjusting screw which is provided with a sleeve graduated to read micrometrically on a scale on the body. In such devices heretofore much difiiculty has been encountered in the joint or point of attachment to the head of the extension rod which,

due to its long leverage, when moved against opposing surfaces was subject to loosening strains which sometimes resulted in breakage. My invention therefore contemplates as one improvement the more positive seating of the anvil of an extension rod as upon the face of a seat to which it is drawn and held by novel means as 20 herein disclosed.

These extension rods. are provided at their outer ends with' little adjustable anvils. Heretofore after a few adjustments these anvils tended to become loose and it became impossible 25 to hold a correct over-all setting. My present invention contemplates as a second improvement means for ensuring a positive and tight interlock of rod and end anvil after, as well as before adjustment of the anvil. 30 With these and other improvements, my invention provides for novel combinations and features long needed but unsupplied by the art.

As illustrative of my inventionlhave shown in the accompanying drawing embodiments well 35 adapted to practical service and capable of quantity production on a basis of extreme. accuracy.

I Throughout the specification and drawing like reference characters are employed to indicate corresponding parts, and in the drawing: 4 Fig. 1 is a side view of a micrometer head without attachments.

Fig. 2 is a view of an extension rod according to my invention.

4 Fig. 3 is a view of a short nut for clamping an extension rod to the head. I

Fig. 4 is a view of a substitute or replacement nut to be used with a hollow sleeve for spacing the rod.

50 Fig. 5 isa view of such a sleeve separate from the nut.

Fig. 6 is a side view of a head with rod attached with the short nut of Fig. 3.

Fig. 7 isa similar view of a head with the long 55 nut holding the rod and spacing sleeve, and

or on'the end face l2" of the collar I2.

Fig. 8 is a longitudinal section through a fragment of thecontacttip of a rod end. As will be seen in the drawing I may provide a conventional micrometer head having a barrel I and sleeve 2 carrying the usual screw, which being internal .does not .appear, but whichhas an axial bore to receive "the reduced stem portions of the rods beyond their seating anvils ill. The

1 end def the head is formed as a cross grooved bearing seat .4 for the rod seating anvils and is surrounded by .an externally threaded .zone .5 ior engagement by a clamping nut.

This clamping nut may be a short cup 6 internally threaded at? for engagement with the zone 5. It is internally shouldered as at it (see Fig. 3) and externally knurled for finger grip, or it may be an elongated clamping piece as shown in Fig. 4. As there shown it consists of a sleeve 10 open-sided as. at H to expose a tubular collar 12 having a knurled exterior engageable through the open sides ll and having a'face l2 frictioned by cross grooves I3. The opposite face I2 is preferably flat. The sleeve Hl also is shouldered'at its outer end as at M and internally threaded as at l for engagement with the zone 5.

The extension rods E6, of different range or over-all length, have an undercut on each side at their attaching anvils H to offer auxiliary collars i'i' engageab-le by the interior end shoulders M of the clamping nuts which are made accessible by radial keyhole slots id. The fiat face of the anvil I! may thus be drawn firmly towards the seat 3 of the micrometer head by the pulling down of the shoulders l4 bearing against the face of the collars ll of the anvil i1 Whether the short nut 6 or elongated clamp ill be used,

a simple tightening up on the knurled finger grip will draw the same and with it the rod it, the anvils I! of which are gripped bythe shoulders 14 of nut 6 or clamp l0.

The extension rods it are provided at their outer ends with anvils l8 which are longitudinally adjustable by means of the axial screws I8 which secure them to the ends of the rods. As before indicated, after a few adjustments these anvils become loose and the accuracy of the instrument becomes impaired. To overcome this difficulty I provide the cupped nut it having fiat sides IQ for engagement by a spanner or other tool and which has a threaded portion which as shown in Fig. 8 engages the threads of the screw l8 between the end of the rod and the anvil. When tightened this cupped nut I9 draws the anvil l8 tightly and evenly against the end of the rod as a seat. When adjustments are to be made the nut I9 is simply unloosened, the anvil adjusted, and the nut l9 re-tightened. This ensures as tight and rigid an interlock of rod end and anvil after as before adjustment.

There is an axial contact 2| at the end of the micrometer sleeve 2 provided with a point having carefully ground contact face 22. The micrometer head has the usual knurled studs 23 protecting the micrometer sleeve from accidental contacts.

Inside micrometers according to my invention afford great accuracy in getting internal lineal measurements of cylinders and rings, and for setting calipers, comparing gages, as well as measuring parallel surfaces.

What I therefore claim and desire to secure by Letters Patent is:

1. An extension rod attachment for an inside micrometer having a hollow externally threaded bearing terminating at one end in an outwardly facing anvil seat, comprising an internally threaded hollow nut engaging said bearing, and an extension rod clamped by said nut within said bearing, said nut having a reduced outwardly extending longitudinally slotted portion terminating in a pair of oppositely disposed inturned shoulders spaced apart from each other by said slot, and said rod having between its ends a generally oblong seating anvil presenting a pair of shoulders at its two opposite shorter edges which when the anvil is entered through the slot of said nut and the rod partially rotated relative to the nut are lodged behind the shoulders of said nut and draw the anvil axially towards said anvil seat when the nut is tightened.

2. The structure of claim 1, and a contact anvil having a shank threaded into the working end of said rod and having a head of less diameter than said rod, and a nut threaded to the shank of said contact anvil and having an outwardly facing cupped portion receiving the head of said anvil.

3. The structure of claim 1 and a hollow spacer disposed between said anvil and anvil seat.

4. An extension rod attachment for an inside micrometer having a hollow externally threaded bearing terminating at one end in an outwardly facing anvil seat, comprising an internally threaded hollow nut engaging said bearing and having at its outer end a longitudinally slotted shouldered portion, and an extension rod having between its ends a seating anvil of less dimension in one direction than that of said nut aperture to provide portions for entrance through the slot of said nut and on partial rotation of the rod relative to the nut for lodgement behind the shoulders of the nut thereby to draw the anvil axially towards said anvil seat when the nut is tightened.

CLIFTON BIGWOOD. 

